Method and apparatus for feedback error detection in a wireless communications systems

ABSTRACT

Errors in closed loop transmit diversity (CLTD) feedback signaling may be detected and/or corrected by a mobile station, according to aspects of the present invention, based on signals received from a base station. The mobile station is generally configured to compute antenna weights to be applied at the base station and feed back corresponding antenna control bits to the base station, as in conventional CLTD systems. However, rather than automatically process subsequent transmissions received from the base station as if the base station properly received the antenna control bits and applied the computed antenna weights, the mobile station attempts to determine the antenna weights actually applied at the base station, and uses these determined antenna weights for processing the subsequent transmissions. Accordingly, even if a feedback signaling error occurred, resulting in the base station using the wrong antenna weights, the mobile station may properly process the transmissions. According to some aspects of the present invention, the base station transmits (feeds forward) antenna control bits actually received from the mobile station on a feed forward channel, and the mobile station processes subsequent transmissions using antenna weights generated based on the fed forward antenna control bits.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication Ser. No. 60/355,471 filed on Feb. 7, 2002, and U.S.Provisional Application Ser. No. 60/357,004 filed on Feb. 13, 2002.

FIELD OF INVENTION

[0002] The present invention relates to wireless communications systemsand, more particularly, to controlling transmissions from multiple basestation antennas through closed loop transmit diversity (CLTD).

DESCRIPTION OF THE BACKGROUND ART

[0003] In prior art code division multiple access (CDMA) systemsutilizing closed loop transmit diversity (CLTD), base stations havingmultiple antennas use an antenna weight coefficient vector to adjust thephase and/or relative amplitude of signals transmitted from eachantenna. In such systems, a mobile station computes a set of optimizedantenna weight coefficients that should be applied at the base stationantennas to maximize the mobile received signal power. The mobilestation then feeds back to the base station a set of antenna controlbits for use by the base station in generating the optimized antennaweights.

[0004] However, one problem associated with CLTD schemes is thatsignaling errors on a feedback channel from the mobile station to thebase station can lead to the use of the wrong antennas weights, whichmay have catastrophic results. For example, if a mobile station“blindly” processes (e.g., decode/demodulate) a transmission receivedfrom a base station on an assumption that the transmission was sentusing antenna weights generated using the antenna control bitspreviously fed back to base station, feedback signaling errors mayresult in the mobile station demodulating/decoding the transmissionusing wrong antenna weights, which may lead to a very low demodulatedsignal-to-noise ratio, and a worthless, or invalid signal. This can leadto retransmissions, resulting in a reduction of bandwidth, and may evenlead to data corruptions.

SUMMARY OF THE INVENTION

[0005] The disadvantages heretofore associated with the prior art, areovercome by the present invention of improved methods and apparatus forfeedback error detections. A mobile station is generally configured tocompute antenna weights to be applied at the base station and feed backcorresponding antenna control bits to the base station, as inconventional CLTD systems. However, rather than automatically processsubsequent transmissions received from the base station as if the basestation properly received the antenna control bits and applied thecomputed antenna weights, the mobile station attempts to determine theantenna weights actually applied at the base station, and uses thesedetermined antenna weights for processing the subsequent transmissions.Accordingly, even if a feedback signaling error occurred, resulting inthe base station using the wrong antenna weights, the mobile station mayproperly process the transmissions. According to some aspects of thepresent invention, the base station transmits (feeds forward) antennacontrol bits actually received from the mobile station on a feed forwardchannel, and the mobile station processes subsequent transmissions usingantenna weights generated based on the fed forward antenna control bits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The teachings of the present invention can be readily understoodby considering the following detailed description in conjunction withthe accompanying drawings, in which:

[0007]FIG. 1 shows an exemplary wireless communications system includinga base station and mobile station in accordance with aspects of thepresent invention;

[0008]FIG. 2 shows a flow diagram of exemplary operations for antennacontrol that may be performed by the mobile station of FIG. 1;

[0009]FIG. 3 shows a flow diagram of exemplary operations for antennacontrol that may be performed by the base station of FIG. 1;

[0010]FIG. 4 shows an exemplary data exchange session in accordance withaspects of the present invention;

[0011]FIG. 5 shows a flow diagram of exemplary operations for providingfeedback information that may be performed by the mobile station of FIG.1;

[0012]FIG. 6 shows another exemplary data exchange session in accordancewith aspects of the present invention;

[0013]FIG. 7 shows another exemplary wireless communications systemincluding a base station and mobile station in accordance with aspectsof the present invention;

[0014]FIG. 8 shows another exemplary data exchange session in accordancewith aspects of the present invention;

[0015]FIG. 9 shows a flow diagram of exemplary operations for feedbackerror detection that may be performed by the mobile station and basestation of FIG. 7;

[0016]FIG. 10 shows a flow diagram of exemplary operations for feedbackerror detection that may be performed by the mobile station of FIG. 7;

[0017]FIG. 11 shows another flow diagram of exemplary operations forfeedback error detection that may be performed by the mobile station ofFIG. 7;

[0018]FIG. 12 shows still another flow diagram of exemplary operationsfor feedback error detection that may be performed by the mobile stationof FIG. 7;

[0019] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon to the figures.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention provides methods, apparatus, and systemsfor performing transmit diversity in a wireless communications system.According to some aspects of the present invention, encoded antennacontrol information may be transmitted (fed back) from a mobile stationto a base station. The base station may decode the antenna controlinformation and use the decoded antenna control information to generatea set of antenna weights calculated to optimize transmitted signalstrength received by the mobile station. According to some aspects, theencoded antenna control information may be interleaved in a singlefeedback control channel with channel quality information. According toother aspects of the present invention, feedback errors may be detectedand/or corrected at the mobile station.

[0021] As used herein, the term closed loop transmit diversity (CLTD)generally refers to any transmit diversity scheme where feedback from amobile station is used to control (e.g., adjust phase and/or power of)antennas used for transmissions to the mobile station, and specificallyincludes selection transmit diversity (STD). As used herein, powercontrol generally refers to the setting/adjusting of relative antennatransmit amplitudes. As used herein, a channel generally refers to acommunication link established between a transmitting device and areceiving device. For example, in CDMA networks, communications channelsare typically established by using an agreed-upon spreading code at thetransmitting and receiving devices.

[0022] The following merely illustrates aspects of the presentinvention. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements which, although notexplicitly described or shown herein, embody aspects of the presentinvention and are included within its spirit and scope. Furthermore, allexamples and conditional language recited herein are principallyintended expressly to aid the reader in understanding the aspects of thepresent invention and the concepts contributed by the inventors tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions. Moreover, allstatements herein reciting principles, aspects, and embodiments of theinvention, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

[0023] Thus, for example, it will be appreciated by those skilled in theart that the block diagrams herein represent conceptual views ofillustrative circuitry embodying the principles of the invention.Similarly, it will be appreciated that any flow charts, flow diagrams,pseudocode, and the like represent various processes which may besubstantially represented in computer readable medium and so executed bya computer or processor, whether or not such computer or processor isexplicitly shown. Further, various functions of the various elementsshown in the FIGs., may be provided through the use of dedicatedhardware as well as hardware capable of executing software inassociation with appropriate software. When provided by a processor, thefunctions may be provided by a single dedicated processor, by a singleshared processor, or by a plurality of individual processors, some ofwhich may be shared. Moreover, explicit use of the term “processor” or“controller” should not be construed to refer exclusively to hardwarecapable of executing software, and may implicitly include, withoutlimitation, digital signal processor (DSP) hardware, read-only memory(ROM) for storing software, random access memory (RAM), and non-volatilestorage. Other hardware, conventional and/or custom, may also beincluded.

[0024] In the claims hereof any element expressed as a means forperforming a specified function is intended to encompass any way ofperforming that function including, for example, a) a combination ofcircuit elements which performs that function or b) software in anyform, including, therefore, firmware, microcode or the like, combinedwith appropriate circuitry for executing that software to perform thefunction. The invention as defined by such claims resides in the factthat the functionalities provided by the various recited means arecombined and brought together in the manner which the claims call for.Applicant thus regards any means which can provide those functionalitiesas equivalent as those shown herein.

TRANSMIT DIVERSITY BASED ON ENCODED FEEDBACK

[0025]FIG. 1 illustrates the primary elements in a wirelesscommunication system 100 employing transmit diversity in accordance withaspects of the present invention. As illustrated, the wirelesscommunications system 100 includes a base station 110 in communicationwith a mobile station 120 via a forward (downlink) channel 132. Ofcourse, while only a single base station 110 and mobile station 120 areshown, the wireless communications system 100 may include a plurality ofeach. According to some aspects of the present invention, the wirelesscommunications system 100 may be capable of operating in accordance withany number of well known standards, such as the Universal MobileTelecommunications System (UMTS) standard, the CDMA 2000 standard andtheir evolutions, which are hereby incorporated by reference in theirentireties.

[0026] The base station 110 includes one or more antennas 112 (forillustrative purposes, two antennas 112, and 1122, are shown) fortransmitting signals on the forward channel 132. The antennas 112receive signals from a transmitter portion 114 of the base station 110.As illustrated, the transmitter portion 114 may include conventionalcomponents, such as a channel encoder 111 to receive and encode signalsto be transmitted, such as control and data signals. Encoded signalsfrom the encoder 111 are received as input by a spreader multiplier 113,which multiplies the received signals by selected spreading codes.Copies of spread signals from the spreader multiplier 113 are receivedas input by weight multipliers 115 ₁ and 115 ₂ where the signals aremultiplied by antenna weights w₁ and w₂ in order to adjust the phaseand/or amplitude of the spread signals. The weighted signals from theweight multipliers 115 ₁ and 115 ₂ are combined with pilot signals bycombiners 117 ₁ and 117 ₂. Each of the combined signals are thentransmitted to the mobile station 120 via a respective one or theantennas 112 ₁ and 112 ₂.

[0027] As illustrated, the mobile station 120 generally includes one ormore antenna 122 (one is shown), a receiver portion 124, channel qualityestimator 126, weight calculator 128, and feedback encoder 129.Operations of the mobile station 120, and the illustrated componentstherein, may be best described concurrently with reference to FIG. 2,which illustrates exemplary operations 200 for controlling transmitdiversity that may be performed at the mobile station 120, in accordancewith the principles of the present invention. However, it should benoted that the illustrated components of the mobile station 120 of FIG.1 are exemplary only and other elements may also be capable ofperforming the operations 200. Further, the elements shown in the mobilestation 120 of FIG. 2 may also be capable of operations other than theexemplary operations 200.

[0028] The operations 200 begin at step 202, for example, when the basestation 110 transmits a signal or signals to the mobile station 120. Theoperations 200 may be entered in step 202 with every transmission (e.g.,within a time slot) from the base station 110, or periodically, forexample, every N time slots, where N may correspond to a transmissiontime interval (TTI) or may be otherwise predetermined, for example,depending on how often feedback is desired. Regardless, at step 204, themobile station 120 receives signals transmitted from the base stationantennas 112 via antenna 122, which may be fed to the receiver 124,which may process (e.g., demodulate, decode, etc.) the signals usingwell known techniques.

[0029] At step 206, the mobile station 120 determines the channelquality based on the received signals. For example, the received signalsmay be fed from the receiver 124 to the channel quality estimator 126 todetermine channel quality. The channel quality estimator 126 maycalculate a channel quality information using well known measures, suchas signal to noise ratio (SNR) and signal to interference and noiseratio (SINR).

[0030] At step 208, the mobile station 120 calculates antenna weights tobe applied at the base station, based on the received signals. Forexample, the received signals may be fed from the receiver 124 to theantenna weight calculator 128 to calculate the antenna weights. Theantenna weights may be a matrix of complex valued signals. As previouslydescribed, the antenna weights (e.g., w₁ and w₂) are generallycalculated in an effort to maximize the strength of the signals receivedat the mobile station 120, and may be calculated using well knowntechniques.

[0031] However, in accordance with aspects of the present invention, andin contrast to the prior art, rather than attempt to maximize thestrength of signals received from more than one base station (e.g., in asoft handoff situation) the antenna weights may be calculated tomaximize the received signal strength from only a primary base station110. However, channels used in HSDPA applications are not subject tosoft handoff, and the HSDPA channels are only supported by a primarybase station. Therefore, by calculating antenna weights in an effort tomaximize the received signal strength from only the primary basestation, degradation of signal strength (received from the primary basestation) due to calculating the antenna weights to maximize receivedsignal strength from other base stations (not supporting the datachannels) may be avoided.

[0032] At step 210, the mobile station 120 generates a feedback messagecontaining channel quality information (CQI) or antenna controlinformation (ACI). For example, the feedback encoder 129 may begenerally configured to receive channel quality output from the channelquality estimator and antenna weights from the antenna weight calculatorand generate the feedback message with the CQI or ACI.

[0033] For example, to conserve bandwidth and reduce feedback delays,rather than feed back the entire matrix of antenna weights, the mobilestation 120 may feed back a set of antenna control information (ACI)bits generated by the feedback encoder based on the antenna weights (forexample through simple quantization of the weight values). The ACI bitsare generally designed to provide sufficient information for the basestation 110 to generate the antenna weights calculated by the mobilestation weight calculator 128. For example (as with CLTD modes supportedin UMTS), the ACI bits may include a certain number of bits for phasecontrol, and a certain number of bits for power control (i.e., settingof the relative antenna transmit amplitudes). The number of bits mayvary with different implementations and may be determined, for example,based on a desired resolution of phase and/or amplitude control. Forexample, the ACI bits may include 3 bits for phase control and 2 bitsfor amplitude control, providing for 8 different phase control settingsand 4 different amplitude settings, respectively.

[0034] Of course, while a greater number of bits generally provides agreater resolution, the number of feedback bits may be subject to thelaw of diminishing return. In other words, additional feedback bits mayrequire a feedback message to be transmitted over additional time slots,increasing the feedback delay, which may outweigh a marginal increase inperformance. Further, in selection transmit diversity only one of aplurality of antennas is chosen for transmission. Accordingly, theantenna control information may simply provide an indication of theselected antenna (e.g., one of 2^(N) antennas may be selected with N ACIbits).

[0035] Regardless of the exact format and type of the ACI, however, inaccordance with aspects of the present invention, and in contrast to theprior art, ACI may be sent in the feedback message as a set of encodedbits over one or more time slots, with multiple feedback bits per slot.Thus, the feedback message containing the ACI may include redundancy andmay, therefore, be transmitted at lower power than conventional CLTDantenna control information.

[0036] In further contrast with the prior art, for some embodiments ofthe present invention, the same feedback channel 134 may be used tofeedback both ACI and CQI. As will be discussed in greater detail below,if a common feedback channel is used, for a given set of time slots usedfor transmitting the feedback message, whether the feedback messagecontains CQI or ACI may be determined by a variety of algorithms.

[0037] At step 212, the mobile station 120 transmits the feedbackmessage to the base station 110 and, at step 214, the operations 200 areterminated, for example, prior to repeating the operations 200 for asubsequent transmission. (Of course, while not shown, the mobile station120 also includes a transmitter, which may include any combination ofwell known components.) The base station 110 may receive the feedbackmessage and process the feedback message to extract the feedbackinformation (ACI or CQI) to be used to control future transmissions tothe mobile station 120.

[0038] For example, the base station 110 may receive and process thefeedback message according to exemplary operations 300, illustrated inFIG. 3. The operations 300 begin at step 302, for example, after thebase station 110 has transmitted a signal to the mobile station 120 andis waiting to receive a feedback message.

[0039] At step 304, the base station 110 receives the feedback messageand, at step 306, extracts the feedback information from the feedbackmessage. For example, the feedback signal containing the feedbackmessage may be fed to a feedback decoder 119 generally configured todecode the feedback message and extract the feedback information.

[0040] At step 308, the base station 110 determines whether the feedbackinformation (FBI) contains channel quality information (CQI) or antennacontrol information (ACI), which may also be performed by the feedbackdecoder 119. Determination of whether the FBI contains CQI or ACI maydepend on the format of the FBI. For some embodiments, the CQI and ACImay be transmitted using a same number of encoded bits. In fact, the CQIand ACI may be transmitted in the same FBI field (e.g., transmitted inan agreed upon set of time slots) of the feedback channel 134.Therefore, the CQI and ACI may each be allocated a certain number of thepossible values of the FBI bit field.

[0041] For example, if the FBI field includes a total number of 6 bits,there are 64 possible values, which may be allocated between ACI and CQIas desired. As illustrated in TABLE I below, 32 of the 6-bit FBI values(e.g., 000000-011111) may be allocated to ACI and 32 values (e.g.,100000-111111) for CQI, in which case a most significate bit (MSB) maybe tested to determine if the FBI field contains ACI or CQI. TABLE I FBIFORMAT EXAMPLE (CLTD) 6-bit FBI Signaling 000000 32 levels for channelquality information (CQI) 000001 . . . 011111 100000 32 levels forantenna control information (ACI) 110001 . . . 111111

[0042] As an alternative, any other type of allocation may also be used(e.g., 48 values for CQI and 16 values may for ACI). The specificallocation of FBI values to ACI and CQI may be determined by animplementer, for example, based on system requirements and capabilities.

[0043] For some embodiments, selection transmit diversity may beemployed where one of the two antennas is selected for transmission atany given time. The mobile station 120 may select an antenna fortransmission based on pilot signals received from the two antennas.Therefore, the ACI may simply contain information indicating theselected antenna. Accordingly, the possible FBI values may be allocatedbetween the CQI and antenna selection. As illustrated in TABLE II, asingle bit TABLE II FBI FORMAT EXAMPLE (STD) 6-bit FBI Signaling 00000062 levels for channel quality information (CQI) 000001 . . . 111101111110 2 levels for antenna selection 111111

[0044] is sufficient to indicate the selected antenna (e.g., a 0 in theLSB may indicate selection of antenna 1, while a 1 in the LSB mayindicate antenna 2). Accordingly, the FBI may be compared against athreshold value corresponding to the maximum value of CQI (or ACI) todetermine if the FBI contains CQI or ACI.

[0045] Regardless of the particular format, if the FBI contains ACI,operations proceed to step 310, where the antennas are adjusted usingthe extracted antenna control information. For example, the base stationmay include an antenna weight generator 116 configured to generate a setof antenna weights (e.g., weight vectors w1 and w2), based on theextracted ACI bits. As illustrated, the generated antenna weights may beapplied at the weight multipliers 115 for future transmissions from theantennas 112.

[0046] Alternately, if the FBI contains CQI, operations proceed to step312, to schedule and select transport format (TF) of futuretransmissions using the extracted channel quality information. Transportformat selection may include various signaling decisions made based onthe channel quality, such as a number of data bits and redundant bits toencode in each data transmission time slot. At step 314, the operations300 are terminated.

[0047] Of course, the operations 200 and 300 may be repeated by themobile station 120 and base station 110, respectively, to continuouslyadjust transmissions from the base station 110 during an exchange ofdata (or data session). For example, FIG. 4 illustrates a flow oftraffic for an exemplary data session, in accordance with aspects of thepresent invention. As illustrated, feedback messages containing channelquality information (CQI) and antenna control information (ACI) may beinterleaved in the feedback channel 134. For example, CQI may betransmitted in slots 0 and 1 (slots 6 and 7, etc.), while ACI istransmitted in slots 3 and 4 (slots 9 and 10, etc.).

[0048] The feedback channel 134 may be an existing channel (e.g.,defined by one of the previously referenced standard), such as a controlchannel used for uplink (UL) signaling. An example of such a controlchannel is the high speed dedicated physical control channel (HS-DPCCH)defined for use in HSDPA. The HS-DPCCH is presently used for HSDPArelated UL signaling such as ACK/NACK (AN) feedback and CQI. Inaccordance with HSDPA, the mobile station 120 may be required toacknowledge receipt of data packets from the base station 110.Therefore, ACK/NACK (AN) signaling may also be interleaved in thefeedback channel 134. As illustrated, according to HSDPA, a data packetis transmitted in a transmission time interval (TTI) of three timeslots. Of course, the actual TTI length may vary with different (e.g.,non HSDPA) implementations of the present invention.

[0049] As illustrated, the feedback bits (for either CQI or ACI) may betransmitted every TTI (e.g., for 6 bits of FBI, 3 bits may betransmitted per slot for 2 slots of a 3-slot TTI). Thus, the basestation 110 may make adjustments based on the received feedback, priorto the transmitting the next data packet in the following TTI. Forexample, ACI transmitted in slots 3 and 4 (TTI 2) may be used by thebase station 110 to adjust antennas 112 for data transmitted in slots6-8 (TTI 3). Similarly, CQI transmitted in slots 0 and 1 (TTI 1) may beused for scheduling and transport format (TF) selection fortransmissions in slots 3-5 (TTI 2). This corresponds to a feedback cycleof 2 TTI (or 6 time slots). In other words, the mobile station mayexpect to see transmissions adjusted based on the feedback 2 TTI afterproviding the feedback.

[0050] The decision about whether to send CQI or ACI in a particular TTImay be made according to any suitable scheduling scheme. For example,CQI and ACI may each be sent periodically (for example, every other TTIas illustrated in FIG. 4). As an alternative, the decision about sendingCQI or ACI may be made dynamically based on a relative change of CQIand/or ACI compared to the previous update. Factors that may affectestimated channel quality and calculated antenna weights include achanging distance between the mobile station and base station (e.g., thespeed of the mobile station), interference, and the like.

[0051]FIG. 5 illustrates exemplary operations 500 for dynamicallydetermining whether to send CQI or ACI. The operations 500 begin at 502,for example, after estimating channel quality and calculating antennaweights (e.g., steps 206 and 208 of FIG. 2). At step 504, the mobilestation calculates a change in channel quality (ΔCQ). At step 506, themobile station calculates a change in antenna weights (ΔAW).

[0052] For example, the changes in channel quality may be calculated bysimply comparing the current estimated channel quality to the previousestimated channel quality. As an alternative, the change in channelquality may be calculated based on the current estimated channel qualityand the estimated channel quality of a number of previous time slots.Similar techniques may be applied to calculate the change in antennaweights over one or more time slots.

[0053] At step 508, the mobile station 120 determines if the calculatedchange in channel quality exceeds a threshold value (T_(CQ)). If so, afeedback message is generated containing CQI, at step 510. If thecalculated change in channel quality does not exceed T_(CQ), the mobilestation 120 determines if the calculated change in antenna weightsexceeds a threshold value (T_(AW)), at step 512. If so, a feedbackmessage is generated containing ACI, at step 514.

[0054] At step 516, if neither the change in channel quality nor thechange in antenna weights exceeds their corresponding threshold levels,a feedback message containing either ACI or CQI, as determined by adefault schedule, may be generated. For example, the default schedulemay be designed to ensure that both CQI and ACI are fed backoccasionally (for example, every 10 ms). At step 518, the operations 500are terminated, for example, and the generated feedback message may betransmitted.

[0055] As an alternative to interleaving CQI and ACI on the same controlchannel, for some embodiments, CQI and ACI may be transmitted from themobile station 120 to the base station 110 using separate feedbackchannels. For example, as illustrated in FIG. 6, CQI may be transmittedon a first feedback channel 134 ₁, while ACI is transmitted on a secondfeedback channel 134 ₂. As illustrated, the second feedback channel 134₂ may be dedicated to ACI feedback. The second feedback channel 134 ₂may also use a different spreading (or channelization) code than thefirst feedback channel 134 ₁. Accordingly, transmissions from the twochannels are orthogonal and both channels may be decoded at the basestation. The frequency of ACI feedback on the second feedback channel134 ₂ may vary (e.g., every TTI, every N TTIs, etc.), and may becontrolled through any suitable signaling procedures, such as throughthe control channel 133.

[0056] Regardless, by utilizing two feedback channels 134, and 134 ₂,both ACI and CQI may be provided to the base station with minimal delay.Therefore, an advantage to using separate feedback channels 134 ₁, and134 ₂ may include a reduced feedback cycle time. Another advantage maybe that use of the previously described HSDPA control channel (HS-DPCCH)may be maintained, without modification, for CQI signaling, which mayhelp speed implementation (e.g., by taking advantage of existinghardware, software, etc.).

[0057] Of course, for some embodiments, a feedback message may includeboth ACI and CQI. For example, the feedback information may have N+Mbits, with N bits allocated to ACI and M bits allocated to CQI. Ofcourse, using this approach, an increased number of bits would requirean additional number of bits to be transmitted to achieve the samenumber of possible values for each ACI or CQI. For example, to achieve32 possible values for each ACI and CQI, FBI would require 10 bits (5for each), rather than the 6 required using the allocation techniquedescribed above. However, because the ACI and CQI arrive together, thetotal feedback cycle time may be reduced. Further, as previouslydescribed, the ACI and CQI bits may be encoded and, thus, may betransmitted at a lower transmission power level, which may result inless interference and increased battery life.

[0058] Regardless of the number of feedback channels utilized and theformat of the feedback message (e.g., FBI values allocated between ACIand CQI, encoded, unencoded, etc.), feedback signaling errors may leadto a base station receiving the wrong feedback information, which maylead to transmissions using wrong antenna weights or transmissions fromthe wrong antenna, resulting in high error rates at the mobile station.

FEEDBACK ERROR DETECTION/CORRECTION

[0059] In an effort to provide a level of robustness (i.e., tolerance tofeedback signaling errors), embodiments of the present invention providefor detection of, and possible recovery from, feedback errors. Accordingto aspects of the present invention, the mobile station may determine aset of antenna weights applied at the base station and process areceived transmission accordingly, regardless of the antenna controlinformation fed back to the mobile station. While the feedback errordetection techniques described below may be utilized in conjunction withthe closed loop transmit diversity (CLTD) schemes described above, theyare not so limited, and may also be utilized in systems employing anyother type CLTD schemes, such as UMTS CLTD modes.

[0060]FIG. 7 illustrates an exemplary wireless communications system 700comprising a base station 710 and a mobile station 720 employingfeedback error detection, according to one aspect of the presentinvention. As illustrated, the base station 710 may transmit data to themobile station 720, via a data channel 732, while the mobile station 720feeds back antenna control information (ACI_(FB)) to the base station710 via a feedback channel 734 for use in controlling transmissions fromone or more base station antennas 712.

[0061] If the feedback bits received at the base station 710 are inerror, then the wrong weights are applied to the antennas. If the mobilestation 720 assumes that the weights being used are indeed the ones thatit fed back to the base station 710, then the result will be improperdemodulation at the mobile station receiver resulting, almost certainly,in a frame error event at the mobile station 720. Therefore, it isimportant not only to ensure that the feedback error rate is low butalso that, when the wrong weights are applied as a consequence, themobile station 720 is able to detect that the weights are incorrect. Ifthe mobile station 720 detects that the weights used by the base station710 are incorrect, it can demodulate the received signal with theweights actually used by the base station 710. The result will be a lossin signal-to-noise ratio (because the calculated antenna weights fedback to the base station 710 were not used), but not as catastrophic asthe case when mobile station 720 uses weights for demodulation that aredifferent from the ones used by the base station 710.

[0062] To alleviate this problem, in accordance with aspects of thepresent invention, and in contrast to the prior art, the base station710 may also send (feed forward) antenna control information (ACI_(FF))to the mobile station, via a feed forward channel 736. The ACI_(FF) mayindicate the antenna and weight information the base station 720 usedfor transmissions in the data channel 732. For some embodiments, thefeed forward channel 736 may be an existing channel, such as a UMTSdefined control channel (or more specifically, an HSDPA defined controlchannel) used for downlink signaling.

[0063]FIG. 8 illustrates a flow of traffic for an exemplary datasession, in accordance with aspects of the present invention, utilizingthe feed forward channel 736. As illustrated, ACI_(FF) may be sent onthe feed forward control channel 736 prior to sending a transmission onthe data channel 732, using antenna weights indicated by the ACI_(FF).Therefore, the mobile station 720 may use ACI_(FF) to verify the antennacontrol information previously fed back (ACI_(FB)) to the base station710 was received without error and/or whether the base station 710 hasused antenna weights specified by the ACI_(FB) for transmissions yet.Accordingly, the ACI_(FF) may allow the mobile station 720 to detectfeedback errors or delays in applying antenna weights specified by theACI_(FB).

[0064]FIG. 9 illustrates exemplary operations 900 that may be performedby the base station 710 and the mobile station 720 for performingfeedback error detection, according to aspects of the present invention.The operations of steps 902-910 may correspond to conventional CLTDoperations or to the previously described CLTD operations according tothe present invention.

[0065] At steps 902 and 904, the base station 710 broadcasts and themobile station 720 receives, respectively, pilot signals. At step 906,the mobile station 720 calculates antenna weights and correspondingantenna control information bits based on the pilot signals. Typically,the base station 710 continually broadcasts pilot signals from eachantenna. The mobile station 720 typically uses these pilot signals todetermine the appropriate antenna weights. At step 908, the mobilestation transmits a feedback message containing the antenna controlinformation (ACI_(FB)) to the base station 710. At step 910, the basestations 710 receives the feedback message (i.e., receives the feedbackmessage with or without errors) and extracts the ACI bits.

[0066] At step 912, the base station 710 transmits (feeds forward)antenna control information (ACI_(FF)) to the mobile station 720. Inother words, the ACI_(FF) may simply be the ACI extracted from thefeedback message and “echoed” back to the mobile station 720. As analternative, the ACI_(FF) may be the ACI used to generate the antennaweights used for the next data transmission. For example, the basestation 710 may not have received the latest ACI fed back from themobile station 720 in time for application to the next datatransmission. Therefore, the ACI_(FF) may provide an indication of theantenna weights used for a subsequent transmission. Regardless, at step914, the mobile station 720 receives ACI_(FF).

[0067] At step 916, the base station 710 transmits data to the mobilestation 720 using antenna weights generated using the ACI_(FF). At step918, the mobile station 720 receives the data, and processes (e.g.,demodulates, decodes, etc.) the data based on the ACI_(FF), rather thanthe ACI_(FB). For some embodiments, the mobile station 720 may alsocompare ACI_(FB) to ACI_(FF) to verify the base station 710 received theACI_(FB), for example, to detect or record feedback errors for controlpurposes. For example, in response to detecting a high error rate on afeedback channel (as indicated by mismatches between ACI_(FB) toACI_(FF)), the mobile station may request a new feedback channel.

[0068] For some embodiments, the mobile station 720 may perform feedbackerror detection/correction even if the base station 710 does not feedforward antenna control information. For example, the mobile station 720may estimate the antenna weights used by the base station from adedicated antenna pilot channel received with a transmission. (Referringback to FIG. 8, data is typically transmitted in a time slot preceded bya pilot signal).

[0069] In the absence of a feed-forward mechanism, the mobile station720 needs to use signals received from common pilot channels of the twoantennas and dedicated pilot channels of the two antennas. The commonpilot channels do not use any weights, but the dedicated pilot channelsuse the same antenna weights as the data to be transmitted to the user.By correlating the common pilot channel signal with the dedicated pilotchannel signal from the antennas, the weights applied can be inferred(of course, this process is not completely error free). When the set ofpossible weights is large, inferring the antenna weights used at thebase station 710 is a complex task. Thus, the use of a feed-forwardmechanism greatly simplifies verification of the weights used. However,in the absence of the feed-forward mechanism, the inferred weights maystill be used to correct feedback errors.

[0070]FIG. 10 illustrates exemplary operations 1000 for correctingfeedback errors that may be performed by the mobile station 720 in theabsence of a feed forward ACI from the base station 710. The operationsbegin at step 1002, for example, after receiving a transmission from thebase station 710.

[0071] At step 1004, the mobile station calculates antenna weights andcorresponding antenna control information (ACI) bits. At step 1006, themobile station 720 transmits a feedback message containing the ACI_(FB)bits to the base station 710. At step 1008, the mobile station receivesa transmission with a dedicated pilot signal from the base station.Because there is no feed forward information regarding the antennaweights applied at the base station for the transmission, there is noexplicit way for the mobile station 720 to determine if a feedbacksignaling error has occurred.

[0072] Therefore, at step 1010, the mobile station 720 estimates theantenna weights used by the base station 710 based on the dedicatedpilot signals. At step 1012, the mobile station 720 demodulates/decodesthe transmission using the estimated antenna weights rather than thecalculated antenna weights. Accordingly, the mobile station 720 mayproperly process the transmission even if a feedback signaling error hasoccurred.

[0073] Of course, although the mobile station 720 may not use thepreviously calculated antenna weights (fed back to the base station 710)to process the transmission, it is still desirable to calculate theweights and feed the antenna control information back to the basestation 710 in an effort to optimize the received signal strength.Further, as previously described, estimating antenna weights from thepilot signal may also provide an indication of whether antenna weightscorresponding to feedback ACI have yet been applied by the base station,thus possibly overcoming feedback delays.

[0074]FIG. 11 illustrates another technique that may be used to detectfeedback errors in systems utilizing selection transmit diversity (STD).Rather than simply demodulate/decode a received transmission using aselected antenna that was requested in a feedback message, the mobilestation demodulates/decodes the received transmission multiple times: asif it came from ANT1 and as if it came from ANT2. The antennacorresponding to a demodulated transmission with the highest signal tonoise ratio (SNR) is selected for future decoding/demodulating. Themethod begins at step 1102, for example, after requesting the basestation transmit from a particular antenna in an STD feedback message.

[0075] At step 1104, the mobile station 720 receives a transmission fromthe base station 710 having one or more antennas (e.g., ANT1 and ANT2),each antenna broadcasting one or more pilot signals. At step 1106, themobile station 720 demodulates/decodes the transmission using separatechannel estimates generated based on each pilot signal to generate twoseparate demodulated signals. As previously described, each antenna maybroadcast common and dedicated pilot signals. The common or dedicatedpilot signals received from the base station can be appropriatelyfiltered to determine the channel estimates to be used for demodulation.

[0076] At step 1108, the mobile station 720 calculates a signal to noiseratio (SNR) for each of the demodulated signals (e.g., SNR1 and SNR2).At step 1110, the mobile station 720 compares the two calculated SNRs.If SNR1>SNR2, the mobile station 720 assumes the base station 710transmitted the signal using ANT1, and the mobile station 720 selectsANT 1 for channel estimation and demodulation of subsequenttransmissions, at step 1112. On the other hand, if SNR2>SNR1, the mobilestation 720 assumes the base station transmitted the signal using ANT2,and the mobile station 720 selects ANT2 for channel estimation anddemodulation of subsequent transmissions, at step 1114. At step 1116,the operations 1100 are terminated, for example, by returning theselected antenna to a main control routine.

[0077] According to the operations 1100, the antenna corresponding to apilot signal used for a channel estimate resulting in a demodulatedsignal with the greatest SNR is selected for subsequent channelestimation and demodulation, regardless of which antenna was selected ina previously fed back ACI. Of course, the operations 1100 may be easilymodified to accommodate a base station 710 with more than two antennas.Of course, the operations 1100 may be repeated as necessary, forexample, following transmission of each STD feedback message from themobile station 720 to the base station 710.

[0078] Often, certain types of transmissions are sent with an errorchecking value, such as a cyclic redundancy check (CRC). Therefore, asan alternative to calculating SNR as a means to gather informationregarding transmissions from the base station 710, the mobile station720 may calculate a CRC for a set of signals generated by demodulating areceived transmission using different combinations of antenna weights.FIG. 12 illustrates exemplary operations 1200 that may be performed bythe mobile station 720 for gathering information regarding transmissionsfrom the base station 710 based on calculated CRCs.

[0079] The exemplary operations 1200 may be used to detect/correctfeedback errors in systems utilizing any type of CLTD. In other words,the illustrated technique may be used to detect/correct errors infeeding back antenna control information including antenna selections orantenna weight information (e.g., phase and/or power controlinformation). The description below refers to a cyclic redundancy check(CRC), as just one example of an error detection value and theoperations 1200 may be easily modified to accommodate any other type oferror correction value (e.g., other types of checksums, parity bits,etc.).

[0080] The operations 1200 begin at 1202, for example, after feedingback antenna control information (ACI) to a base station. At step 1204,the mobile station 720 receives a transmission including a CRC. Asindicated by for-block 1206, steps 1208-1214 represent a loop ofoperations that may be performed for each combination of antenna weights(e.g., each combination of antenna control bits, whether they be antennaselection bits, phase/power bits, etc.).

[0081] At step 1208, a combination of antenna weights is chosen and, atstep 1210, the received transmission is demodulated/decoded using thechosen combination of antenna weights. At step 1212, the mobile station720 calculates a CRC for the demodulated/decoded transmission. At step1214, the calculated CRC is checked to see if it has passed or failed(e.g., if the calculated CRC matches the received CRC).

[0082] If the CRC passes this indicates that the presently chosencombination of antenna weights were applied at the base station whensending the transmission. Therefore, if the CRC passes, the loop (steps1208-1214) is exited, the chosen combination of antenna weights isselected for demodulating/decoding subsequent transmissions, at step1216, and the operations are terminated, at step 1220, for example, byreturning the selected combination of antenna weights to a main controlroutine.

[0083] If the CRCs do not match, processing returns to the for-block1206, and a new combination of antenna weights is chosen, at step 1208.If the operations 1208-1214 are performed for each combination ofantenna weights without a match between CRCs, an error likely occurred(in transmission or reception of the feedback message). Accordingly,processing proceeds to step 1218, where the transmission is discarded,prior to terminating the operations, at step 1220 and, for example,returning an error code (e.g., a flag indicating a feedback signalingerror has been detected) to a main control routine.

[0084] The mobile station 720 may choose to traverse the possiblecombinations of antenna weights (within the loop of the for-block 1206)in any order, according to any suitable method. For example, the mobilestation 720 may simply start with the combination of antenna weightscorresponding to a lowest value of ACI bits (e.g., all 0s) and proceedin order to the highest value (e.g., all 1s).

[0085] As an alternative, the mobile station 720 may employ a“historical” approach, for example, by first choosing a combination ofantenna weights corresponding to the most recently fed back ACI, then acombination of antenna weights corresponding to the second most recentlyfed back ACI, etc. In other words, in the absence of a feedbacksignaling error, the base station should have used recently fed back ACIfor generating antenna weights used for the received transmission.Therefore, this historical approach may result in choosing the correctcombination of antenna weights with reduced processing time. On theother hand, for some embodiments, some of the operations 1200 may beperformed in parallel (e.g., the decoding/demodulation and comparisonsof steps 1210 and 1212), so processing time may not be an issue.

[0086] Although various embodiments that incorporate the teachings ofthe present invention have been shown and described in detail herein,those skilled in the art can readily devise many other variedembodiments that still incorporate these teachings.

We claim:
 1. A method for use in a mobile station, comprising the stepsof: generating antenna control information for use at a base stationbased on one or more signals received from the base station;transmitting the antenna control information to the base station;receiving antenna control information from the base station; andprocessing subsequent signals received from the base station accordingto the antenna control information received from the base station. 2.The method of claim 1, further comprising the step of comparing thegenerated antenna control information to the antenna control informationreceived from the base station to detect a feedback signaling error. 3.The method of claim 1, wherein said step of generating comprisesgenerating antenna weights to be applied to signals transmitted from thebase station.
 4. The method of claim 3, wherein the antenna controlinformation comprises a set of bits for use in generating the antennaweights at the base station.
 5. The method of claim 4, wherein the setof bits comprises at least two bits for phase control and at least twobits for relative transmit amplitude control.
 6. The method of claim 1,wherein said step of generating comprises selecting one of the basestation antennas to be used for sending signals from the base station tothe mobile station.
 7. A method for use in a base station havingmultiple antennas, comprising the steps of: receiving antenna controlinformation from a mobile station; transmitting the received antennacontrol information to the mobile station; and transmitting one or moresignals to the mobile station in accordance with the received antennacontrol information.
 8. The method of claim 7, wherein said step oftransmitting one or more signals to the mobile station in accordancewith received antenna control information comprises the steps of:generating a set of antenna weights based on the antenna controlinformation; and applying the antenna weights to the one or moresignals.
 9. The method of claim 7, wherein said step of transmitting oneor more signals to the mobile station in accordance with receivedantenna control information comprises transmitting the one or moresignals from a selected one of the multiple antennas specified by theantenna control information.
 10. A method for use in a mobile station,comprising the steps of: generating antenna weights for use at a basestation; transmitting antenna control information indicative of thegenerated antenna weights to the base station; receiving one or moresignals from the base station; estimating, based on the one or moresignals, antenna weights applied at the base station in transmitting theone or more signals; and processing the one or more signals according tothe estimated antenna weights.
 11. The method of claim 10, wherein saidstep of estimating comprises the step of estimating antenna weightsapplied at the base station based on pilot signals broadcast by each ofthe base station antennas.
 12. The method of claim 10, furthercomprising the step of comparing the estimated antenna weights to thegenerated antenna weights to detect a feedback signaling error.
 13. Amethod for use in a mobile station, comprising the steps of: selectingone of a plurality of antennas for use in transmitting signals from abase station; transmitting antenna control information indicative of theselected antenna to the base station; receiving one or more signals fromthe base station; determining which of the base station antennas wasused for transmitting the one or more signals from the base station; andprocessing subsequently received signals from the base station as if thesubsequently received signals were transmitted using the determined basestation antenna.
 14. The method of claim 13, wherein said step ofdetermining which of the base station antennas was used for transmittingthe one or more signals comprises the steps of: generating a set ofprocessed signals, each processed signal generated by processing the oneor more signals as if the one or more signals were transmitted from acorresponding one of the base station antennas; calculating a signal tonoise ratio for each of the processed signals; and determining a basestation antenna corresponding to the processed signal with the highestcalculated signal to noise ratio was used for transmitting the one ormore signals.
 15. The method of claim 13, wherein said step ofprocessing subsequently received signals from the base station comprisesthe step of performing channel estimation based on a pilot signalbroadcast by the determined base station antenna.
 16. The method ofclaim 13, wherein said step of determining which of the base stationantennas was used for transmitting the one or more signals comprises thesteps of: generating a set of processed signals, each processed signalgenerated by processing the one or more signals as if transmitted from acorresponding one of the base station antennas; calculating an errordetection value for each processed signal; and determining a basestation antenna corresponding to a processed signal for which acalculated error detection value matches an error detection valueincluded with the one or more signals was used for transmitting the oneor more signals.
 17. A method for use in a mobile station, comprisingthe steps of: receiving one or more signals from a base station;determining a set of antenna weights applied at the base station intransmitting the one or more signals based on a set of processedsignals, each processed signal generated by processing the one or moresignals according to a different set of antenna weights; and processingthe one or more signals according to the determined set of antennaweights.
 18. The method of claim 17, wherein said step of determiningcomprises: calculating an error detection value for each processedsignal; and determining a set of antenna weights corresponding to aprocessed signal for which the calculated error detection value matchesan error detection value included with the one or more signals was usedfor transmitting the one or more signals.
 19. The method of claim 17,wherein: the antenna control information comprises a field having arange of values, each corresponding to a different set of antennaweights; and each processed signal is generated by processing the one ormore signals according to a set of antenna weights corresponding to avalue of the antenna control information field.
 20. The method of claim17, wherein said step of determining the antenna weights applied at thebase station comprises calculating a signal to noise ratio for each ofthe processed signals.
 21. The method of claim 17, further comprisingthe steps of: transmitting to the base station, prior to said step ofreceiving one or more signals from the base station, antenna controlinformation indicative of a set of generated antenna weights to beapplied at the base station; and comparing the determined set of antennaweights to the generated antenna weights to verify the base stationproperly received the antenna control information transmitted to thebase station.
 22. A mobile station comprising: means for generatingantenna weights to be applied at a base station having a plurality ofantennas; means for transmitting antenna control information indicativeof the generated antenna weights to the base station; means fordetermining, based on one or more signals received from the basestation, antenna weights applied at the base station in transmitting theone or more signals; and means for processing the one or more signals orsubsequent signals as if transmitted from the base station using thedetermined antenna weights.
 23. The mobile station of claim 22, furthercomprising means for comparing the generated antenna weights to thedetermined antenna weights to verify the base station properly receivedthe antenna control information.
 24. The mobile station of claim 22,wherein the one or more signals comprise a feed forward messagecontaining antenna control information indicative of the antenna weightsapplied at the base station.
 25. The mobile station of claim 22, whereinthe means for determining is configured to generate a set of processedsignals, each generated by processing the one or more signals as iftransmitted from the base station using a different set of antennaweights.
 26. The mobile station of claim 25, wherein the means fordetermining is configured to determine the antenna weights applied atthe base station based on signal to noise ratios calculated for the setof processed signals.
 27. The mobile station of claim 25, wherein themeans for determining is configured to determine the antenna weightsbased on error detection values calculated for the set of processedsignals and an error detection value transmitted within the one or moresignals.
 28. A base station comprising: a plurality of antennas; meansfor receiving, from a mobile station, a feedback message includingantenna control information indicative of antenna weights to be used fortransmissions from the plurality of antennas; and means fortransmitting, to the mobile station, a feed forward message includingthe antenna control information, as received in the feedback message,and for subsequently transmitting one or more signals to the mobilestation from the plurality of antennas using the antenna weightsindicated by the antenna control information.
 29. The base station ofclaim 28, wherein the base station further comprises a weight generatorfor generating a set of antenna weights based on a set of encoded bitsincluded in the antenna control information.
 30. The base station ofclaim 28, wherein the antenna control information indicates a selectedone of the plurality of antennas to be used for transmitting the one ormore signals.